Calculate percentage in mySQL where SUM is already present in the table

Question

I have a table(Which I have no control over) like this:

As, you can see this already has total calculate in a separate row I have to do calculate percentage which should look something like this:

The issue is how do I pass Total in a sub query like SELECT Marks from <TABLE> WHERE Topic = 'Total';

, so that I only get a single row?

Thanks

Answer 1

You can do something along the lines of

SELECT m1.*, ROUND(m1.marks / m2.marks * 100, 2) percentage
  FROM marks m1 join marks m2
    ON m1.name = m2.name AND m2.topic = 'Total'
 ORDER BY name, topic

Output:

| Name |   Topic | Marks | percentage |
|------|---------|-------|------------|
|  Joe |    Chem |    43 |      26.38 |
|  Joe |   Maths |    75 |      46.01 |
|  Joe | Physics |    45 |      27.61 |
|  Joe |   Total |   163 |        100 |
...

SQLFiddle